The primary objective of this research proposal is to provide fundamental information on the stereochemical properties of the nucleic acid constituents--mononucleosides, mononucleotides, dinucleosides, cyclic nucleotides, rare nucleosides and nucleotides of tRNA, nucleotide analogues with antiviral activity including the class of molecules with arabinose sugars. The x-ray diffraction studies are supplemented by conformational energy calculations to gain further insight into the stereochemical constraints on nucleosides and nucleotides and the interrelationship that exists between the sugar ring conformation and the sugar-base glycosyl and sugar-phosphate backbone conformations.